MRI involving forwardly and reversely polarised RF excitation

Abstract

A system for MR imaging of a body placed in an examination volume including main coils for establishing a substantially homogeneous main magnetic field in the examination volume, gradient coils for generating switched magnetic field gradients superimposed upon the main magnetic field, RF coils for radiating RF signals towards the body, a controller for controlling the generation of the magnetic field gradients and the RF signals, a processor for forming MR images from received MR signal samples, and an object having an RF antenna for receiving RF signals generated by the RF coils which are configured to generate circularly polarized RF signals having a selectable sense of rotation.

The invention claimed is: 
     
       1. A system for Magnetic Resonance (MR) imaging of a body placed in an examination volume, the system comprising:
 a first coil configured to establish a substantially homogeneous main magnetic field in the examination volume; 
 a second coil configured to generate switched magnetic field gradients superimposed upon the main magnetic field; 
 a third coil configured to radiate circularly polarized RF signals towards the body; 
 a controller coupled to the first, second and third coils and configured to control the generation of the magnetic field gradients and a direction of circular polarization of the RF signals generated by the third coil to be selectable between forward polarization and reverse polarization; 
 a receiver configured to receive and sample MR signals; 
 a processor configured to form MR images from the MR signal samples; and 
 an object having an RF antenna configured to receive RF signals generated by the third coil. 
 
     
     
       2. The system of  claim 1 , wherein the controller is configured to generate a series of first RF signals having a forward circular polarization for exciting nuclear magnetization within the body. 
     
     
       3. The system of  claim 1 , wherein the controller is configured to generate at least one second RF signal having a reverse circular polarization for inducing a voltage within the RF antenna of the object without exciting nuclear magnetization within the body. 
     
     
       4. The system of  claim 3 , wherein the processor is configured to acquire a localization signal generated by the object as a response to the second RF signal and to compute the position of the object from the localization signal. 
     
     
       5. The system of  claim 1 , wherein the object is an interventional instrument comprising a solenoid coil and a capacitor forming a resonant RF as the RF antenna. 
     
     
       6. The system of  claim 1 , wherein the object is an MR surface coil. 
     
     
       7. The system of  claim 1  wherein the third coil comprises a plurality of RF coils forming a multi-coil array, each RF coil being driven by at least one of an individual RF amplifier and an individual RF waveform generator. 
     
     
       8. A method for Magnetic Resonance (MR) imaging of at least a portion of a body placed in an examination volume of an MR system, the method comprising acts of:
 exciting nuclear magnetization within the body by generating with a first coil a first RF signal, the first RF signal having a forward circular polarization, 
 switching the first coil to generate at least one second RF signal having a reverse circular polarization inducing a voltage within an RF antenna of an auxiliary equipment of the MR system without exciting nuclear magnetization within the body, 
 acquiring MR signals from the body, and 
 reconstructing an MR image from the acquired MR signals. 
 
     
     
       9. The method of  claim 8 , wherein the method comprises acts of acquiring a localization signal generated by the auxiliary equipment as a response to the second RF signal and computing the position of the auxiliary equipment within the examination volume from the localization signal. 
     
     
       10. The method of  claim 8 , comprising an act of generating a local field having a linear polarization by the voltage within the RF antenna thereby exciting a nuclear magnetization within the body tissue in a vicinity of the RF antenna. 
     
     
       11. A computer program stored on a non-transitory computer readable medium that when executed by a processor configures the processor to perform a method for operating a Magnetic Resonance (MR) system, wherein the computer program comprises instructions for performing acts of:
 generating with a first coil a first RF signal having a forward circular polarization for exciting nuclear magnetization, 
 switching the first coil to generate a second RF signal having a reverse circular polarization for inducing a voltage within an RF antenna of an auxiliary equipment of the MR system without exciting nuclear magnetization. 
 
     
     
       12. A processor configured to perform a method for operating a Magnetic Resonance(MR) system, the method comprising acts of:
 generating through a first coil a first RF signal having a forward circular polarization for exciting nuclear magnetization, 
 switching the first coil to generate a second RF signal having a reverse circular polarization for inducing a voltage within an RF antenna of an auxiliary equipment of the MR system without exciting nuclear magnetization.